Optical switch incorporating stepped faceted mirrors

ABSTRACT

An optical switch that includes optical paths organized into a set of M input optical paths and a set of N output optical paths. The optical switch additionally includes a faceted mirror corresponding to each of the M input optical paths and including N facets and a faceted mirror corresponding to each of the N output optical paths and including M facets. Finally, the optical switch includes a moving mechanism coupled to each faceted mirror to step the faceted mirror to selectively align one of the facets of the faceted mirror with the one of the optical paths with which the faceted mirror is associated. The facets of each of the faceted mirrors corresponding to one of the sets of optical paths, i.e., the set of input optical paths or the set of output optical paths, are preferably angled to reflect light towards a different one of the faceted mirrors corresponding to the other of the sets of optical paths, i.e., the set of output optical paths or the set of input optical paths, respectively.

FIELD OF THE INVENTION

The invention relates to optical switches and, in particular, to an M×Noptical switch in which the optical signals are switched using stepped,faceted mirrors.

BACKGROUND OF THE INVENTION

MEMS-based M×N optical switches are currently being developed for use inoptical switching systems, such as the optical switching systems used toswitch optical signals from one optical fibre to another in an opticalnetwork. In such an optical switch, an optical signal received via aninput fibre illuminates a first steerable mirror. The input fibre is oneof M input fibres. The first steerable mirror is associated with theinput fibre and steers the optical signal towards a second steerablemirror. The second steerable mirror is associated with an output fibre.The output fibre is one of N output fibres. The second steerable mirrorreflects the optical signal received from the first steerable mirrorinto the output fibre.

In such an optical switch, the angle of each of the steerable mirrorsmust be accurately set to a precision in the order of 1 part in 2¹³ tocouple the optical signal from the input fibre to the output fibre witha high coupling efficiency. When the input and output fibres are arrayedin two-dimensional arrays, the angle of the steerable mirrors must beset with the required precision about each of two orthogonal axes.Complex, closed-loop positioning mechanisms are required to achieve thisaccuracy.

SUMMARY OF THE INVENTION

The invention provides an optical switch comprising optical pathsorganized into a set of M input optical paths and a set of N outputoptical paths. The optical switch additionally comprises a facetedmirror corresponding to each of the M input optical paths and includingN facets and a faceted mirror corresponding to each of the N outputoptical paths and including M facets. Finally, the optical switchcomprises a moving mechanism coupled to each faceted mirror to step thefaceted mirror to selectively align one of the facets of the facetedmirror with the one of the optical paths with which the faceted mirroris associated.

The facets of each of the faceted mirrors corresponding to one of thesets of optical paths, i.e., the set of input optical paths or the setof output optical paths, are angled to reflect light towards a differentone of the faceted mirrors corresponding to the other of the sets ofoptical paths, i.e., the set of output optical paths or the set of inputoptical paths, respectively.

The optical switch according to the invention avoids the need to set theangle of steerable mirrors with great accuracy by replacing each of thesteerable mirrors of the conventional MEMS-based optical switch with astepped, faceted mirror. Each facet of the mirror is fabricated with therequired angular precision, but the mirror is simply stepped linearly inone or two directions, or rotationally, to align the appropriate facetof the faceted mirror with the input optical path or the output opticalpath. The precision with which the mirror needs to be stepped issubstantially less than that with which the angles of the steerablemirrors need to be set. This simplifies and reduces the cost of makingthe optical switch according to the invention. Moreover, the steps withwhich each of the mirrors is moved can be made equal to one another.This enables a simple electrostatic stepper motor to be used as themoving mechanism, which further simplifies and reduces the cost of theoptical switch according to the invention compared with a conventionaloptical switch.

The invention additionally provides a method for switching an opticalsignal received via an input optical path to an output optical path. Theinput optical path is any one of an array of M input optical paths andthe output optical path is any one of an array of N output opticalpaths. In the method, an N-faceted mirror corresponding to each of the Minput optical paths and an M-faceted mirror corresponding to each of theN output optical paths are provided. Each N-faceted mirror is locatedopposite the corresponding one of the input optical paths. EachM-faceted mirror is located opposite the corresponding one of the outputoptical paths. The N-faceted mirror corresponding to the input opticalpath is stepped to align one of the facets thereof with the inputoptical path. The facet aligned with the input optical path is angled toreflect the optical signal towards the M-faceted mirror corresponding tothe output optical path. The M-faceted mirror corresponding to theoutput optical path is stepped to align one of the facets thereof withthe output optical path. The facet aligned with the output optical pathis angled to reflect light that would be received via the output opticalpath towards the N-faceted mirror corresponding to the input opticalpath.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a simplified first embodiment ofan optical switch according to the invention. The optical switch isshown configured to switch an optical signal from the input optical path20 to the output optical path 32.

FIG. 2A is an enlarged schematic side view of a first embodiment of anexemplary one of the faceted mirrors of the optical switch shown in FIG.1.

FIG. 2B is an enlarged schematic side view of a second embodiment of anexemplary one of the faceted mirrors of the optical switch shown in FIG.1.

FIG. 3A is a schematic diagram showing the simplified embodiment of theoptical switch shown in FIG. 1 reconfigured to switch an optical signalfrom the input optical path 20 to the output optical path 30.

FIG. 3B is a schematic diagram showing the simplified embodiment of theoptical switch shown in FIG. 1 reconfigured to switch an optical signalfrom the input optical path 20 to the output optical path 31.

FIG. 3C is a schematic diagram showing the simplified embodiment of theoptical switch shown in FIG. 1 reconfigured to switch an optical signalfrom the input optical path 20 to the output optical path 33.

FIG. 4A is a schematic diagram showing the simplified embodiment of theoptical switch according to the invention partially reconfigured toswitch an optical signal from the input optical path 21 to the outputoptical path 32.

FIG. 4B is a schematic diagram showing the simplified embodiment of theoptical switch according to the invention fully reconfigured to switchthe optical signal from the input optical path 21 to the output opticalpath 32.

FIG. 5 is a schematic diagram showing a simplified second embodiment ofan optical switch according to the invention.

FIGS. 6A and 6B are enlarged schematic elevation and plan views of anembodiment of an exemplary one of the faceted mirrors of the opticalswitch shown in FIG. 5.

FIG. 7 is a schematic diagram showing a simplified third embodiment ofan optical switch according to the invention. The optical switch isshown configured to switch an optical signal from the input optical path20 to the output optical path 32.

FIG. 8A is a schematic diagram showing the simplified embodiment of theoptical switch shown in FIG. 7 reconfigured to switch an optical signalfrom the input optical path 20 to the output optical path 30.

FIG. 8B is a schematic diagram showing the simplified embodiment of theoptical switch shown in FIG. 7 reconfigured to switch an optical signalfrom the input optical path 20 to the output optical path 31.

FIG. 8C is a schematic diagram showing the simplified embodiment of theoptical switch shown in FIG. 7 reconfigured to switch an optical signalfrom the input optical path 20 to the output optical path 33.

FIG. 9 is a flow diagram illustrating the method according to theinvention for switching an optical signal.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a simplified first embodiment 10 of an optical switchaccording to the invention. The optical switch is composed of the set 12of M input optical paths, the set 14 of N output optical paths, afaceted mirror corresponding to each of the M input optical paths andhaving N facets, a faceted mirror corresponding to each of the N outputoptical paths and having M facets, and a moving mechanism coupled toeach faceted mirror to linearly step the faceted mirror to align one ofthe facets of the faceted mirror with the optical path to which thefaceted mirror corresponds.

In the example shown in FIG. 1, the set 12 of input optical paths iscomposed of the three input optical fibres 20, 21 and 22 arranged as aone-dimensional array disposed in the x-direction, and the set 14 ofoutput optical paths is composed of the four output fibres 30, 31, 32and 33 also arranged in a one-dimensional array disposed in thex-direction. The set 13 of output optical paths is located opposite theset 12 of input optical paths in the same plane, and is offset from theset of input optical paths in the x-direction and in the y-direction.Locating the output optical paths and the input optical paths in thesame plane simplifies the design of the faceted mirrors, but is notessential to the invention.

Located opposite the light-emitting ends of the input fibres 20, 21 and22 are the faceted mirrors 40, 41 and 42 respectively. Each of thefaceted mirrors is located to receive light from a different one of theinput fibres, and is said to correspond to the input fibre. In theexample shown, the set 14 of output optical paths is composed of fouroptical fibres, so the faceted mirrors 40-42 each have four facets.

Located opposite the ends of the output fibres 30, 31, 32 and 33 are thefaceted mirrors 50, 51, 52 and 53, respectively. Each of the facetedmirrors is located in a position at which it would receive light from adifferent one of the output fibres if light were output from the outputfibres, and is said to correspond to the output fibre. In the exampleshown, the set 12 of input optical paths is composed of three opticalfibres, so the faceted mirrors 50-53 each have three facets.

The number of facets stated above are minimum numbers. It may bedesirable for the faceted mirrors to have more than the minimum numberof facets stated above. For example, when the number of input opticalpaths differs from the number of output optical paths, providing thefaceted mirrors corresponding to the larger set of optical paths withthe same number of facets as the faceted mirrors corresponding to thesmaller set of optical paths allows the same mirror design to be used incorresponding positions with both the output optical paths and the inputoptical paths. This would also allow the numbers of input optical pathsor output optical paths to be increased later, for example. However,facets in excess of the minimum numbers stated above will be unused.

The fibres constituting the set 12 of input optical paths and the set 13of output optical paths, the faceted mirrors 40-42 and the facetedmirrors 50-53 are mounted on a suitable armature (not shown) thatprecisely defines their positions relative to one another.

FIG. 2A is an enlarged view of a first embodiment of the faceted mirror40 shown in FIG. 1. The faceted mirror is composed of the stage 60 onwhich are mounted the four mirror facets 61, 62, 63 and 64 arranged in aone-dimensional array disposed in the x-direction. The stage is movablymounted on the stator 67 in a manner that allows the stage to movefreely in the x-direction, but which constrains the stage from moving inthe y- and z-directions. For example, high aspect ratio bendableflexures (not shown) may extend between the stage and the stator toallow the stage to move freely in the x-direction but to restrainmovement of the stage in the y- and z-directions.

The faceted mirrors 41 and 42 are similarly configured to the facetedmirror 40 and are similarly mounted on the stage 67. The faceted mirrors50-53 are also similarly configured and are similarly mounted on thestator 68.

Disposed between the stage 60 and the stator 67 is the moving mechanismshown schematically at 70. The moving mechanism moves the stage 60, and,hence, the mirror facets 61-64, back and forth in the x-direction, asindicated by the arrows 69. The moving mechanism is preferably aprecision linear electrostatic or electromagnetic stepper motor thatmoves the stage in the x-direction between predetermined positions. Ateach of the predetermined positions, a different one of the mirrorfacets 61-64 is aligned with the light output by the input optical path20. A precision linear electrostatic stepping motor of the typedescribed in U.S. Pat. No. 5,986,381 of Hoen et al. is preferred. Thecenters of the mirror facets are preferably equally spaced in thex-direction to make the distances between the predetermined positionsequal. The electrodes of the Hoen stepping motor can then be fabricatedwith a pitch that enables the stepping motor to move the stageautomatically and precisely to each of the predetermined positions.

Alternatively, the moving mechanism 70 can comprise a rotary motor,preferably a rotary stepper motor, and a suitable transmission thatconverts rotary motion into linear motion. As further alternatives,piezoelectric actuators or piezoelectric benders or other precisionmechanisms that generate linear movement can be used. Such mechanismscan be used with or without feedback control of the position of thestage 60.

The faceted mirrors 41, 42 and 50-53 are each equipped with a movingmechanism similar to the moving mechanism 70.

The mirror facets 61-64 of the faceted mirror 40 are angled differentlyfrom one another such that each of them reflects light received from theinput fibre 20 towards a different one of the faceted mirrors 50-53corresponding to the set 14 of output optical paths. In particular, themirror facets 61, 62, 63 and 64 are angled such that they reflect lightreceived from the input optical path 20 to towards the faceted mirrors50, 51, 52 and 53, respectively, corresponding to the output fibres 31,32, 33 and 34, respectively.

The mirror facets of the faceted mirrors 41 and 42 are also angled tomeet the conditions as those just described. However, since thepositions in the x-direction of the input fibres 21 and 22 correspondingto the faceted mirrors 41 and 42, respectively, differ from one anotherand from that of the input fibre 20, the angles of the mirror facets ofthe faceted mirrors 41 and 42 differ from one another and from those ofthe mirror facets of the faceted mirror 40.

The mirror facets of the faceted mirrors 50-53 corresponding to the set14 of output optical paths are angled such that, if light were output bythe output fibres 30-33, each mirror facet would reflect such lighttowards on a different one of the faceted mirrors 40-42, respectively,corresponding to the set 12 of input optical paths. When angled to meetthe condition just described, each facet of the faceted mirrors 50-53reflects light received from a different one of the faceted mirrors40-42 into the output optical path corresponding to the faceted mirror.

FIG. 1 shows an example in which the optical switch 10 is configured toswitch an optical signal from the input fibre 20 to the output fibre 32.The moving mechanism 70 linearly steps the faceted mirror 40 in thex-direction to align the facet 63 with the input fibre 20. The facet 63reflects the optical signal received from the input fibre 20 towards thefaceted mirror 52 corresponding to the output fibre 32 in the set 14 ofoutput optical paths.

The moving mechanism 82 coupled to the faceted mirror 52 linearly stepsthe moving mirror in the x-direction to align the facet 91 with theoutput fibre 32. The optical signal received via the input fibre 20 andreflected by the faceted mirror 40 is incident on the facet 91 of thefaceted mirror 52. The facet 91 is angled such that it reflects theoptical signal into the output optical path 32.

FIG. 3A shows an example in which the optical switch 10 is reconfiguredto switch the optical signal from the input fibre 20 to the output fibre30. The moving mechanism 70 has linearly stepped the faceted mirror 40in the x-direction to align the facet 61 with the input fibre 20. Themoving mechanism 80 has linearly stepped the faceted mirror 50, whichcorresponds to the output fibre 30, in the x-direction to align thefacet 92 with the output fibre 30.

The facet 61 of the faceted mirror 40 reflects the optical signal outputby the input fibre 20 towards the faceted mirror 50. At the facetedmirror 50, the optical signal is incident on the facet 92, which isangled to reflect the optical signal into the output fibre 30.

FIG. 3B shows an example in which the optical switch 10 is reconfiguredto switch the optical signal from the input fibre 20 to the output fibre31. The moving mechanism 70 has linearly stepped the faceted mirror 40in the x-direction to align the facet 62 with the input fibre 20. Themoving mechanism 81 has linearly stepped the faceted mirror 51, whichcorresponds to the output fibre 31, in the x-direction to align thefacet 93 with the output fibre 31.

The facet 62 of the faceted mirror 40 reflects the optical signal outputby the input fibre 20 towards the faceted mirror 51. At the facetedmirror 51, the optical signal is incident on the facet 93, which isangled to reflect the optical signal into the output fibre 31.

FIG. 3C shows an example in which the optical switch 10 is reconfiguredto switch the optical signal from the input fibre 20 to the output fibre33. The moving mechanism 70 has linearly stepped the faceted mirror 40in the x-direction to align the facet 64 of the faceted mirror 40 withthe input fibre 20. The moving mechanism 83 has linearly stepped thefaceted mirror 53, which corresponds to the output fibre 33, in thex-direction to align the facet 94 with the output fibre 33.

The facet 64 of the faceted mirror 40 reflects the optical signal outputby the input fibre 20 towards the faceted mirror 53. At the facetedmirror 53, the optical signal is incident on the facet 94, which isangled to reflect the optical signal into the output fibre 33.

FIG. 4A shows an example in which the optical switch 10 is part-waythrough being configured from the state shown in FIG. 1 to switch anoptical signal from the input fibre 21 to the output fibre 32. Themoving mechanism 71 of the faceted mirror 41, corresponding to the inputfibre 21, has linearly stepped the faceted mirror 41 in the x-directionto align the facet 95 with the input fibre 21. The facet 95 reflects theoptical signal received via the input fibre 21 towards the facetedmirror 52 that corresponds to the output fibre 32. However, the opticalsignal is incident on the facet 91 of the faceted mirror 52 at adifferent angle of incidence from that of the optical signal shown inFIG.1 as being received via the input fibre 20. Thus, the facet 91reflects the optical signal received via the input fibre 21 with anangle of reflection that results in the optical signal missing theoutput fibre 32.

FIG. 4B shows the optical switch 10 fully reconfigured to switch theoptical signal from the input fibre 21 to the output fibre 32. Themoving mechanism 82 has linearly stepped the faceted mirror 52 in the−x-direction to align the facet 96 with the output optical path 32. Thefacet 96 is angled to reflect the optical signal received from the facet95 of the faceted mirror 41 into the output fibre 32.

It will be apparent to a person of ordinary skill in the art that theoptical switch 10 may be reconfigured by laterally stepping various onesof the faceted mirrors 40-42 and 50-53 to switch an optical signalreceived via any one of the M input fibres to any one of the N outputfibres in a manner similar to the switching operations exemplified inFIGS. 3A-3C, 4A and 4B. It will also be apparent to the person ofordinary skill in the art that the simplified embodiments shown in thisdisclosure can easily be extended to operates with larger arrays ofinput fibres and output fibres and correspondingly larger arrays offaceted mirrors, each faceted mirror having a correspondingly largernumber of facets.

FIG. 5 shows a simplified second embodiment 150 of an optical switchaccording to the invention. Elements of the embodiment 150 thatcorrespond to elements of the embodiment 10 shown in FIG. 1 areindicated by the same reference numerals and will not be described againhere. The optical switch is composed of the set 12 of M input opticalpaths, the set 14 of N output optical paths, a faceted mirrorcorresponding to each of the M input optical paths and having N facets,a faceted mirror corresponding to each of the N output optical paths andhaving M facets, and a moving mechanism coupled to each faceted mirrorto rotationally step the faceted mirror to align one of the facets ofthe faceted mirror with the optical path to which the faceted mirrorcorresponds.

Located opposite the light-emitting ends of the input fibres 20, 21 and22 are the faceted mirrors 140, 141 and 142 respectively. Each of thefaceted mirrors is located to receive light from a different one of theinput fibres, and is said to correspond to the input fibre. In theexample shown, the set 14 of output optical paths is composed of fouroptical fibres, so the faceted mirrors 140-142 each have four facets.

Located opposite the ends of the output fibres 30, 31, 32 and 33 are thefaceted mirrors 150, 151, 152 and 153, respectively. Each of the facetedmirrors is located in a position at which it would receive light from adifferent one of the output fibres if light were fed into the outputfibres, and is said to correspond to the output fibre. In the exampleshown, the set 12 of input optical paths is composed of three opticalfibres, so the faceted mirrors 150-153 each have three facets.

The number of facets stated above are minimum numbers, as noted above.

FIGS. 6A and 6B are enlarged elevation and plan views of an embodimentof the faceted mirror 140 of the optical switch 150 shown in FIG. 5. Thefaceted mirror is composed of the stage 160 on which are mounted thefour mirror facets 61, 62, 63 and 64. The stage is rotationally mountedon the pivot 68 affixed to the stator 67 in a manner that allows thestage to rotate freely between predetermined angular positions, butwhich constrains lateral movement of the stage. The faceted mirrors 141and 142 are similarly configured and are similarly mounted on the stator67. The faceted mirrors 150-153 are similarly configured and aresimilarly pivotally mounted on the stator 168.

Disposed between the stage 60 and the stator 67 is the moving mechanismshown schematically at 170. The moving mechanism moves the stage 60,and, hence, the mirror facets 61-64, rotationally about the pivot 68, asindicated by the arrows 169. The moving mechanism is preferably aprecision rotary electrostatic or electromagnetic stepper motor thatrotates the stage about the pivot between predetermined rotationalpositions. At each of the predetermined rotational positions, adifferent one of the mirror facets 61-64 is aligned with the lightoutput by the input optical path 20. A precision rotary electrostaticstepping motor of the type described in U.S. Pat. No. 5,986,381 of Hoenet al. is preferred. The centers of the mirror facets are preferablyspaced at equal angles about the pivot to make the angles between thepredetermined rotational positions equal. The electrodes of the Hoenrotary stepping motor can then be fabricated with a pitch that enablesthe stepping motor to move the stage automatically and precisely to eachof the predetermined rotational positions.

Alternatively, the moving mechanism 170 can comprise an electromagneticrotary motor, preferably a rotary stepper motor. As furtheralternatives, piezoelectric actuators or piezoelectric benders, and asuitable transmission that converts linear motion into rotary motion orother precision mechanisms that generate rotary movement can be used.Such mechanisms can be used with or without feedback control of therotational position of the stage 160. Such mechanisms can be used withor without a mechanical detent that defines the predetermined rotationalpositions.

The faceted mirrors 41, 42 and 50-53 are each equipped with a rotationalmoving mechanism similar to the moving mechanism 170.

The facets of each of the faceted mirrors corresponding to one of thesets of the optical paths are angled to reflect light towards adifferent one of the faceted mirrors corresponding to the other of thesets of the optical paths, as described above.

FIG. 5 shows an example in which the optical switch 150 is configured toswitch an optical signal from the input fibre 20 to the output fibre 32.The moving mechanism 170 rotationally steps the faceted mirror 140 aboutthe pivot 68 to align the facet 63 with the input fibre 20. The facet 63reflects the optical signal received from the input fibre 20 towards thefaceted mirror 152 corresponding to the output fibre 32 in the set 14 ofoutput optical paths.

The moving mechanism 182 coupled to the faceted mirror 152 rotationallysteps the moving mirror about its pivot to align the facet 191 with theoutput fibre 32. The optical signal received via the input fibre 20 andreflected by the faceted mirror 140 is incident on the facet 191 of thefaceted mirror 152. The facet 191 is angled such that it reflects theoptical signal into the output optical path 32.

It will be apparent to a person of ordinary skill in the art that theoptical switch 150 may be reconfigured by rotating the appropriate onesof the faceted mirrors 140-142 and 150-153 to switch an optical signalreceived via any one of the M input fibres to any one of the N outputfibres in a manner similar to the switching operations exemplified inFIGS. 3A-3C, 4A and 4B. It will also be apparent to the person ofordinary skill in the art that the simplified embodiments shown in thisdisclosure can easily be extended to operates with larger arrays ofinput fibres and output fibres and correspondingly larger arrays ofrotating faceted mirrors, each faceted mirror having a correspondinglylarger number of facets.

In the embodiments of the optical switch according to the inventionshown in FIGS. 1 and 5, the set 13 of output optical paths is mountedopposite the set 12 of input optical paths, and is offset from the setof input optical paths in the x-direction and in the y-direction. Thefaceted mirrors 40-42 or 140-142 are mounted opposite the set 12 ofinput optical paths and offset from the set of input optical paths inthe −y-direction. The faceted mirrors 50-52 or 150-152 are mountedopposite the set 13 of output optical paths and offset from the set ofoutput optical paths in the y-direction

In some applications, it may be more convenient for the input opticalpaths and the output optical paths to be located in a common plane, andfor the faceted mirrors 40-42 or 140-142 and the faceted mirrors 50-52or 150-152 to be located in and mounted on a common plane. FIGS. 7 showsa third embodiment 200 of the optical switch according to the inventionin which the elements of the optical switch 10 shown in FIG. 1 have beenrearranged to place the set 13 of input optical paths in the same planeas the set 12 of input optical paths and offset from the set of inputoptical paths in the y-direction, and to offset the faceted mirrors fromthe optical paths in the −y-direction with the faceted mirrors 50-53offset from the faceted mirrors 40-42 in the x-direction. The embodimentshown in FIG. 5 may be similarly rearranged. Elements of the embodimentshown in FIG. 7 that correspond to elements of the embodiment shown inFIG. 1 are indicated by the same reference numerals and will not bedescribed again here.

The optical switch 200 additionally includes the common mirror 16located between the set 12 of input optical paths and the set 13 ofoutput optical paths and facing the plane in which the faceted mirrorsare located.

FIG. 7 shows an example in which the optical switch 200 is configured toswitch an optical signal from the input fibre 20 to the output fibre 32.The moving mechanism 70 linearly steps the faceted mirror 40 in thex-direction to align the facet 63 with the input fibre 20. The facet 63reflects the optical signal received from the input fibre 20 towards thepoint 75 on the common mirror 16. The optical signal is incident onpoint 75 of the common mirror at an angle of incidence at which thecommon mirror reflects the optical signal towards the faceted mirror 52corresponding to the output fibre 32 in the set 14 of output opticalpaths.

The moving mechanism 82 coupled to the faceted mirror 52 linearly stepsthe moving mirror in the x-direction to align the facet 91 with theoutput fibre 32. The optical signal received via the input fibre 20 andreflected by the faceted mirror 40 and point 72 of the common mirror 16is incident on the facet 91 of the faceted mirror 52. The facet 91 isangled such that it reflects the optical signal into the output opticalpath 32.

FIG. 8A shows an example in which the optical switch 200 is reconfiguredto switch the optical signal from the input fibre 20 to the output fibre30. The moving mechanism 70 has linearly stepped the faceted mirror 40in the x-direction to align the facet 61 with the input fibre 20. Themoving mechanism 80 has linearly stepped the faceted mirror 50, whichcorresponds to the output fibre 30, in the x-direction to align thefacet 92 with the output fibre 30.

The facet 61 of the faceted mirror 40 reflects the optical signal outputby the input fibre 20 towards the point 76 on the common mirror 16. Theoptical signal is incident on the point 76 of the common mirror at anangle of incidence at which the common mirror reflects the opticalsignal towards the faceted mirror 50. At the faceted mirror 50, theoptical signal reflected by the common mirror is incident on the facet92, which is angled to reflect the optical signal into the output fibre30.

FIG. 8B shows an example in which the optical switch 200 is reconfiguredto switch the optical signal from the input fibre 20 to the output fibre31. The moving mechanism 70 has linearly stepped the faceted mirror 40in the x-direction to align the facet 62 with the input fibre 20. Themoving mechanism 81 has linearly stepped the faceted mirror 51, whichcorresponds to the output fibre 31, in the x-direction to align thefacet 93 with the output fibre 31.

The facet 62 of the faceted mirror 40 reflects the optical signal outputby the input fibre 20 towards the point 77 on the common mirror 16. Theoptical signal is incident on the point 77 at an angle of incidence atwhich the common mirror reflects the optical signal towards the facetedmirror 51. At the faceted mirror 51, the optical signal reflected by thecommon mirror is incident on the facet 93, which is angled to reflectthe optical signal into the output fibre 31.

FIG. 8C shows an example in which the optical switch 200 is reconfiguredto switch the optical signal from the input fibre 20 to the output fibre33. The moving mechanism 70 has linearly stepped the faceted mirror 40in the x-direction to align the facet 64 of the faceted mirror 40 withthe input fibre 20. The moving mechanism 83 has linearly stepped thefaceted mirror 53, which corresponds to the output fibre 33, in thex-direction to align the facet 94 with the output fibre 33.

The facet 64 of the faceted mirror 40 reflects the optical signal outputby the input fibre 20 towards the point 78 on the common mirror 16. Theoptical signal is incident on the point 78 of the common mirror at anangle of incidence at which the common mirror reflects the opticalsignal towards the faceted mirror 53. At the faceted mirror 53, theoptical signal reflected by the common mirror is incident on the facet94, which is angled to reflect the optical signal into the output fibre33.

The method 100 according to the invention for switching an opticalsignal received via an input optical path to an output optical path willnow be described with reference to FIG. 9. The input optical path is anyone of an array of M input optical paths. The output optical path is anyone of an array of N output optical paths.

In process 102, an N-faceted mirror corresponding to each of the M inputoptical paths is provided.

In process 104, an M-faceted mirror corresponding to each of the Noutput optical paths is provided.

In process 106, each N-faceted mirror is located opposite the one of theinput optical paths to which it corresponds.

In process 108, each M-faceted mirror is located opposite the one of theoutput optical paths to which it corresponds.

In process 110, the N-faceted mirror located opposite the input opticalpath is stepped to align one of its facets with the input optical path.The facet that is aligned with the input optical path is angled toreflect the optical signal towards the M-faceted mirror located oppositethe output optical path.

Finally, in process 112, the M-faceted mirror located opposite theoutput optical path is stepped to align one of its facets with theoutput optical path. The facet that is aligned with the output opticalpath is angled to reflect light that would be received via the outputoptical path towards the N-faceted mirror located opposite the inputoptical path.

The method may additionally use the process described above withreference to FIG. 3A, for example, to change the output optical path towhich the optical signal received via the input optical path isswitched. The output optical path is changed from the output opticalpath referred to in FIG. 9, which will be called a first output opticalpath, to a second output optical path. The second output optical path isone of the output optical paths different from the first output opticalpath.

The method may additionally use the process described above withreference to FIGS. 4A and 4B, for example, to change the input opticalpath via which the optical signal is received from the input opticalpath referred to in FIG. 9, which will be called a first input opticalpath, to a second input optical path. The second input optical path isone of the input optical paths different from the first input opticalpath.

The invention has been described with reference to an example in whichthe 12 set of input optical paths and the set 14 of output optical pathsare each composed of optical paths arranged in a one-dimensional arraydisposed in the x-direction. However, the optical paths in either orboth of the set of input optical paths and the set of output opticalpaths may be arrayed in a one-dimensional array disposed in a directiondifferent from the x-direction, e.g., the z-direction. When the opticalpaths are arranged in a one-dimensional array disposed in thex-direction, the facets of the faceted mirrors are angled about thez-axis. When the optical paths are arranged in a one-dimensional arraydisposed in the z-direction, the facets of the faceted mirrors areangled about the x-axis. Regardless of the arrangement of the opticalpaths, the faceted mirror corresponding to each optical path is locatedopposite the optical path, as shown in FIGS. 1, 5 and 7.

As a further alternative, the optical paths in either or both of the set12 of input optical paths and the set 14 of output optical paths may bearranged in a two-dimensional array. When the optical paths are arrangedin a two-dimensional array, the faceted mirrors are also arranged in atwo-dimensional array the faceted mirror corresponding to each opticalpath located opposite each optical path, as shown in FIGS. 1, 5 and 7.When the optical paths are arranged in a two-dimensional array, thefacets of the faceted mirrors are angled about two axes. For example,the optical paths may be arranged in a two-dimensional array having rowsparallel to the x-axis and columns parallel to the z-axis, with thefacets of the faceted mirrors angled about the z-axis and the x-axis.

The invention has also been described with reference to an example inwhich the faceted mirrors each comprise more than one reflective surfacearrayed in the x-direction, as shown in FIG. 2A. Each of the reflectivesurfaces provides one of the facets 61-64 of the faceted mirror 40. Thefaceted mirrors may alternatively be configured as shown in FIG. 2B. Inthis, the faceted mirror 40 comprises the single reflective surface 65shaped to provide the facets 61-64 arranged in a one-dimensional arrayin the x-y plane.

The invention has been described with reference to an example in whichthe facets of the faceted mirrors, such as the faceted mirror 40, arearranged in a one-dimensional array arrayed in the x-direction. However,the facets of the faceted mirrors may alternatively be arrayed in thex-z plane in a direction different from the x-direction. For example,the facets may be arrayed in the z-direction. In this case, the movingmechanism 70 preferably moves the faceted mirror in a direction parallelto that in which the facets are arrayed. For example, when the facetsare arrayed in the z-direction, the moving mechanism moves the facetedmirror in the z-direction.

As a further alternative, the facets of the faceted mirrors may bearranged in a two-dimensional array. For example, the facets may bearranged in a two-dimensional array having rows parallel to thex-direction and columns parallel to the z-direction. Specifically, thesingle reflective surface 65 shown in FIG. 2B may be shaped to providefacets arranged in a two-dimensional array that additionally extends inthe z-direction. As another example, a two-dimensional array of facetsmay be obtained by extending of the reflective surfaces shown at 61-64in FIG. 2A in the z-direction and dividing each of the reflectivesurfaces into a one-dimensional array of facets disposed in thez-direction.

In embodiments in which the facets of the faceted mirrors are arrangedin a two-dimensional array, the moving mechanism 70 steps the stage 60in two directions instead of the single direction shown in FIGS. 1 and7. When the facets are arranged in a two-dimensional array having rowsparallel to the x-direction and columns parallel to the z-direction, themoving mechanism steps the stage in the z-direction in addition to thex-direction shown.

The invention has been described with reference to an example in whichthe facets, such as the facets 61-64, of the faceted mirrors have flatsurfaces. However, the facets can additionally be shaped to focus thelight reflected by the facet to optimize the coupling efficiency betweenthe input optical path and the output optical path. Since the opticalpath length between the input optical path and the output optical paththat includes each facet differs, each facet is preferably individuallyshaped to focus the light reflected by the facet optimally for thelength of the optical path in which the facet is located.

The precision of the angles of the facets of the faceted mirrorsdetermines the efficiency of the coupling between the input optical pathand the output optical path. The angle of each facet of each facetedmirror is determined once, when the optical switch is designed, and doesnot change during operation of the optical switch 10. Thus, the couplingefficiency of the optical switch is largely determined by the accuracywith which the faceted mirrors are designed and manufactured. The designprocess generates suitable tooling that is then used to mass-produce thefaceted mirrors at low cost and high repeatability. The faceted mirrors,or components of them, may be manufactured using mature andwell-controlled manufacturing processes. For example, the facetedmirrors, or components of them, may be manufactured from single-crystalsilicon by a micromachining process, or from a suitable plastic materialby molding. Similar processes can be used to make the moving mechanismof each faceted mirror.

Also affecting the coupling efficiency is the accuracy with which thefacet of the faceted mirror is aligned with the input optical path orthe output optical path. The moving mechanism is required to step thefaceted mirror linearly in one or two directions, or rotationally, witha precision that ensures that only the facet that effects the desiredcoupling is aligned with the input optical path or the output opticalpath. The precision required of the moving mechanism is several ordersof magnitude less than that with which the angle of each mirror must bedynamically adjusted in at least one dimension in the conventionalMEMS-based optical switch. The angles of the faceted mirrors of theoptical switch according to the invention are pre-determined at thedesign stage and provide low-loss switching with easy mechanical controland long-term stability.

Although this disclosure describes illustrative embodiments of theinvention in detail, it is to be understood that the invention is notlimited to the precise embodiments described, and that variousmodifications may be practiced within the scope of the invention definedby the appended claims.

We claim:
 1. An optical switch, comprising: optical paths organized intoa set of M input optical paths and a set of N output optical paths; afaceted mirror corresponding to each one of the M input optical paths,the faceted mirror including N facets; a faceted mirror corresponding toeach one of the N output optical paths the faceted mirror including Mfacets; a common mirror located between the input optical paths and theoutput optical path and facing the faceted mirrors; and a movingmechanism coupled to each faceted mirror to step the faceted mirror toselectively align one of the facets of the faceted mirror with the oneof the optical paths to which the faceted mirror corresponds, in which:facets of each of the faceted mirrors corresponding to one of the setsof the optical paths are angled to reflect light to be incident on thecommon mirror at angles of incidence at which the common mirror reflectsthe light towards a different one of the faceted mirrors correspondingto the other of the sets of the optical paths.
 2. The optical switch ofclaim 1, in which: in one of the sets of the optical paths, the opticalpaths are arranged in a one-dimensional array; and the facets of thefaceted mirror corresponding to each one of the optical paths in the oneof the sets are angled about one axis.
 3. The optical switch of claim 1,in which: in one of the sets of the optical paths, the optical paths arearranged in a two-dimensional array; and the facets of the facetedmirror corresponding to each one of the optical paths is the one of thesets are angled about two axes.
 4. The optical switch of claim 3, inwhich the axes are orthogonal to one another.
 5. The optical switch ofclaim 1, in which: the facets of the faceted mirror are arranged in aone-dimensional array having an array direction; and the movingmechanism moves the faceted mirror in a direction parallel to the arraydirection.
 6. The optical switch of claim 5, in which the movingmechanism includes a linear electrostatic stepping motor.
 7. The opticalswitch of claim 1, in which: the facets of the faceted mirror arearrayed in a two-dimensional array having two array directions; and themoving mechanism moves the faceted mirror in two directions, eachparallel to a different one of the array directions.
 8. The opticalswitch of claim 1, in which the moving mechanism includes atwo-dimensional linear electrostatic stepping motor.
 9. The opticalswitch of claim 1, in which the facets of the faceted mirror are curvedto focus light reflected by the facets.
 10. The optical switch of claim9, in which: light passes from one of the input optical paths to one ofthe output optical paths via an optical path that includes one of thefacets of the faceted mirror and whose optical path length depends onthe identity of the one of the input optical paths and identity of theone of the output optical paths; and the one of the facets isindividually curved to focus the light in the optical path in accordancewith the optical path length thereof.
 11. The optical switch of claim 1,in which the moving mechanism steps the faceted mirror linearly.
 12. Theoptical switch of claim 1, in which the moving mechanism steps thefaceted mirror rotationally.
 13. A method for switching an opticalsignal received via an input optical path to an output optical path, theinput optical path being any one of an array of M input optical paths,the output optical path being any one of an array of N output opticalpaths, the method comprising: providing an N-faceted mirrorcorresponding to each one of the M input optical paths and an M-facetedmirror corresponding to each one of the N output optical paths;providing a common mirror; locating each N-faceted mirror opposite thecorresponding one of the input optical paths; locating each M-facetedmirror opposite the corresponding one of the output optical paths;locating the common mirror between the array of input optical paths andthe array of output optical paths, facing the faceted mirrors; steppingthe N-faceted mirror corresponding to the input optical path to alignone of the facets thereof with the input optical path, the one of thefacets aligned with the input optical path being angled to reflect theoptical signal towards the M-faceted mirror corresponding to the outputoptical path; and stepping the M-faceted mirror corresponding to theoutput optical path to align one of the facets thereof with the outputoptical path, the one of the facets aligned with the output path beingangled to reflect light that would be received via the output opticalpath towards the N-faceted mirror corresponding to the input opticalpath, wherein: in providing the N-faceted mirror and the M-facetedmirror, the facets of each of the faceted mirrors corresponding to oneof the sets of the optical paths are angled to reflect light to beincident on the common mirror at angles of incidence at which the commonmirror reflects the light towards a different one of the faceted mirrorscorresponding to the other of the sets of the optical paths.
 14. Themethod of claim 13, in which: the input optical path is a first inputoptical path; the method is additionally for changing the input opticalpath via which the optical signal is received from the first inputoptical path to a second input optical path, the second input opticalpath being one of the input optical paths different from the first inputoptical path; and the method additionally comprises: stepping theN-faceted mirror corresponding to the second input optical path to alignone of the facets thereof with the second input optical path, the one ofthe facets aligned with the second input optical path being angled toreflect the optical signal towards the M-faceted mirror corresponding tothe output optical path, and stepping the M-faceted mirror correspondingto the output optical path to align a different one of the facetsthereof with the output optical path, the different one of the facetsaligned with the output optical path being angled to reflect light thatwould be received via the output optical path towards the N-facetedmirror corresponding to the second input optical path.
 15. The method ofclaim 13, in which: the output optical path is a first output opticalpath; the method is additionally for changing the output optical path towhich the optical signal is switched from the first output optical pathto a second output optical path, the second output optical path beingone of the output optical paths different from the first output opticalpath; the method additionally comprises: stepping the N-faceted mirrorcorresponding to the input optical path to align a different one of thefacets thereof with the input optical path, the different one of thefacets aligned with the input optical path being angled to reflect theoptical signal towards the M-faceted mirror corresponding to the secondoutput optical path; and stepping the M-faceted mirror corresponding tothe second output optical path to align one of the facets thereof withthe second output optical path, the one of the facets aligned with thesecond output optical path being angled to reflect light that would bereceived via the second output optical path towards the N-faceted mirrorcorresponding to the input optical path.
 16. The method of claim 13, inwhich, in stepping the N-faceted mirror, the N-faceted mirror is steppedlinearly; and in stepping the M-faceted mirror, the M-faceted mirror isstepped linearly.
 17. The method of claim 13, in which, in stepping theN-faceted mirror, the N-faceted mirror is stepped rotationally; and instepping the M-faceted mirror, the M-faceted mirror is steppedrotationally.